1. What is easy in Perl might not be easy in PHP. For example, in Perl, your script can close STDERR and STDOUT and re-open them to a file. In PHP, this is not possible, because PHP define these as constants, and you can't redefine constant. Is this tru?

2. PHP is not quite mature compare to Perl. Perl is about 10 years older than PHP. PHP is still growing, and certain things (function interface, etc) are still being refined.

3. PHP is not quite open source, because Zend, the company that initially made PHP, is still somewhat in control of what get into the release, so perhaps there is not enough open source developer contributing to PHP core.

4. PHP was not designed to work from command line. It was initially designed to work with web servers. PHP now works from command line, but I am still skeptical.

5. PHP is not thread-safe. PHP core is thread-safe so it claims to be, and you can specify a flag when you build PHP from source. Doesn't look like Zend want to make PHP thread-safe. Although, I have to agree that, operating system, namely Linux, are trying to make processes as light weight as possible, so there might not be any performance gain. I need to investigate more on this.